Udemy enables anyone to teach and learn online, providing step-by-step instructions from picking a topic to publishing and promoting your course. Instructors can use video, PowerPoint, PDFs, audio, zip files and live classes to build a course and share their expertise. Students can take classes in product development from Mark Zuckerberg of Facebook, entrepreneurship from Marissa Mayer of Google, and language courses from Ivy League professors. Category include business & entrepreneurship, academics, the arts, health & fitness, language, music, technology, games, and more.  Most courses are free; paid courses typically range in price from $5 - $250.